1. Field of the Invention
This invention relates to liquid- or gas-fueled heatable appliances, and more specifically to a portable heated appliance having a catalytic heater.
2. Description of the Related Art
Devices enabling flameless combustion of fuels such as butane or propane are known. One such device is described in U.S. Pat. No. 4,361,133 to Bonnema, the inventor of the present invention. This conventional device includes catalytically-coated quartz wool arranged between two spiral support springs. The quartz wool enables the flameless combustion of a fuel/air mixture and can be utilized in a personal appliance requiring a heat source, such as a curling iron. The catalytic combustion of the fuel/air mixture only occurs when the catalytically active material is heated to a certain activation temperature. An activation device provides the necessary energy to raise the catalyst to the required temperature. The activation device ignites, via a spark or external flame, a fuel/air mixture entering the combustion chamber of the appliance. The flame is extinguished fairly quickly, however the ensuing energy released from the ignition is sufficient to heat the catalytically active material to the activation temperature. Subsequently, flameless combustion of the fuel/air mixture takes place.
This design has suffered from several drawbacks. First, the quartz wool carrier itself is mechanically unstable, and must be fixed carefully to its support springs. Further, fibers from the quartz wool can fall off of the main structure and clog the fuel metering nozzle or other portions of the fuel flow path; this loss of fiber also may result in a reduction of catalytic activity of the quartz wool, since some of the catalytically active material is being lost. Also, the quartz wool does not necessarily heat evenly, resulting in hot spots. Finally, since this device is used in the hair care art, it is subject to many hair care products, e.g., shampoo, hair spray, etc., which are prevalent in the ambient air. These hair care products, particularly those containing silicone, have an adverse effect on the useful life of the catalyst, usually resulting in an unacceptably high amount of energy required to cause flameless combustion.
Another conventional device has been described in U.S. Pat. No. 5,320,089 to Schaefer et al. In this device, instead of quartz wool, an expanded metal foil structure (approximately 0.001 inches thick) is used as the carrier structure for the catalytically active material. A fuel/air mixture is supplied as before, and a spark is applied outside the carrier structure to cause an explosion which heats the catalyst to activation temperature. A subsequent design described in U.S. Pat. No. 5,394,862 to Firalti et al. adds a starter catalyst consisting of a wire or wires attached to the outside of the metal carrier structure to facilitate achievement of the activation temperature.
The Schaefer et al. and Firalti et al. patents describe a metal catalytic substrate that is more rugged than the quartz fiber structure used in the Bonnema patent, yet it is required to have a very low mass and high surface area such that a single explosion of the volume of gas in a container around the catalyst will sufficiently raise its temperature to the point where the catalytic combustion will begin. There remain several disadvantages to this construction. First, the metal substrate described is still a rather delicate structure which would not be easy to manufacture and would be susceptible to damage or misalignment by jostling the appliance. Second, if the catalyst should lose activity, for example, from contamination by hair care products, to the point where the heat of a single explosion will no longer initiate catalytic reaction, then it is impossible to use the appliance. Multiple explosions would not be effective, since the fuel/air mixture must be replenished and be allowed to build up in the combustion chamber between explosions, during which time the catalyst will have cooled. Moreover, the explosion used for ignition takes place outside the tubular catalyst structure. In order to manufacture a safe appliance, a flame arrester must be placed between the exploding volume of the fuel/air mixture and the outside environment. Flame arresters are especially important for heated hair care appliances, because many hair care products are highly flammable.
In light of the above deficiencies of conventional devices, there is a need in the art for a catalytic heating system that is durable, will reliably ignite, is simple to manufacture, and does not require additional flame arresters.